Question

When two bodies make extra smooth then force of friction?
A) Increases
B) Decreases
C) Remain same
D) None

Answer 1

Since friction force is force which opposes the motion. When surfaces become extra smooth the property of opposing the motion increases due to intermolecular binding force at atomic level. Hence net opposing force to resist the relative motion between two surfaces increases.

Complete step by step solution:
Firstly we need to understand friction force , as we know Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
So, more is net resistance to relative motion more will be the friction force.

As per question, when two bodies are extra smooth then two type force encounters that opposes relative motion between extra smooth surface normal friction force and intermolecular binding force at molecular level.
Net frictional force = normal friction force + intermolecular binding force
When the surfaces are rough only normal friction occurs between two bodies but as soon as the surface becomes extra smooth normal friction force decreases but friction force increases due to intermolecular binding force.

Therefore option (A) is correct.

Note: All the forces need to be considered while calculating net force although some forces are significant in some range of distances, here interatomic forces are significant only when surfaces are so close at atomic distance. otherwise these forces are not significant and considered to be zero.